A telecommunication network power system usually includes an ac-dc stage converting the power from the ac utility line to a 48V dc distribution bus and a dc/dc stage converting the 48V dc distribution bus to a plurality of voltage levels for all types of telecommunication loads. A conventional ac-dc stage may comprise a variety of EMI filters, a bridge rectifier formed by four diodes, a power factor correction circuit and an isolated dc/dc power converter. The dc/dc stage may comprise a plurality of isolated dc/dc converters. Isolated dc/dc converters can be implemented by using different power topologies, such as LLC resonant converters, flyback converters, forward converters, half bridge converters, full bridge converters and the like.
Active clamp forward converters are widely adopted for small to medium power level isolated power converters in the telecommunications and data communications industries. Higher efficiency is increasingly demanded in small and medium power level isolated power converters. When active clamp forward converters operate in a synchronous rectifier mode, there may be a dead time period between a turn-on period of forward switch and a turn-on period of a freewheeling switch. More particularly, for example, during the dead time period, the freewheeling switch is not turned on and the forward switch has already been turned off. The output current of the active clamp forward converter is flowing through the body diode of the freewheeling switch. The body diode of a metal oxide semiconductor field effect transistor (MOSFET) device has a higher forward voltage drop and slow reverse recovery characteristic. Such a higher forward voltage drop and slow reverse recovery characteristic may result in extra power losses. An adaptive dead time control mechanism may help to reduce the conduction time of body diodes so as to increase efficiency.